Driving the news:Perhaps most worrisome is the massive pile of highly leveraged debt that continues to grow. Bank of America-Merrill Lynch's monthly survey of fund managers finds that, for the first time since 2009, corporate leverage is the top concern among investors surveyed.

52% of investors said they expect global profits to deteriorate — the most since 2008.

60% surveyed say global growth will weaken in the next 12 months, levels not seen since the financial crisis.

U.S. manufacturing activity dropped in December by the most since October 2008.

The yield spread between 2- and 10-year U.S. Treasury notes is the thinnest since 2007, and the yield on 2- and 3-year notes has already risen above that of 5-year notes, meaning a curve inversion.

UBS estimated in September that there was a "record $4.3 trillion in lower-quality corporate loans and high-yield bonds — up from $2.4 trillion in 2010 — that could ... see rising defaults if the healthy U.S. economy starts to wobble," USA Today reports.

"I view this as the most severe threat to the economy and financial system," Mark Zandi, chief economist of Moody's Analytics, told USA Today in response to the UBS figures.

Former Fed Chair Janet Yellen warned in a recent interview, "I am worried about the systemic risks associated with these loans. There has been a huge deterioration in standards; covenants have been loosened in leveraged lending."

Still, there seems to be a consensus among many in the market that it's not yet time to panic.

"Investors remain bearish, with growth and profit expectations plummeting this month," said Michael Hartnett, BAML's chief investment strategist. "Even so, their diagnosis is secular stagnation, not a recession, as fund managers are pricing in a dovish Fed and steeper yield curve."